1. Field of the Invention
The present invention relates to a musical sound emission apparatus, an electronic musical instrument, a musical sound emitting method, and a storage medium for actualizing polyphonic portamento by which a pitch change can be made with pitch differences among constitutive notes of a played chord being maintained.
2. Description of the Related Art
Conventionally, musical sound emission apparatuses with a portamento function have been known. The portamento function is a function for causing a change from the pitch of a sound being emitted by a previous key press (staring point) to smoothly reach the pitch of a sound to be emitted by a current key press (target value). In one known musical sound emission apparatus, the change speed for portamento is set constant irrespective of a pitch difference between the starting point and the target value, or set according to the pitch difference between the starting point and the target value, whereby the time for portamento is kept constant.
For example, in a technique disclosed in Japanese Patent Application Laid-Open (Kokai) Publication No. 2009-053432, a portamento speed r is calculated according to a standard portamento rate R when a pitch difference is a semitone, a pitch difference T between a starting-point pitch and a target pitch, and an interval dependency coefficient K representing the degree of dependency of the pitch difference I on the portamento speed r. The calculated portamento speed r is added to a current pitch for each predetermined cycle, and the sound is continuously changed to the target pitch. When a quick phrase is being played, the interval dependency coefficient K is set so that portamento is constant in time as much as possible in order to prevent the pitch of the phrase from being delayed. When a slow phrase is being played, the interval dependency coefficient K is set so that the portamento speed is constant. As a result, an optimum portamento effect is provided.
However, the technique disclosed in the above-described Japanese Patent Application Laid-Open (Kokai) Publication No. 2009-053432 is intended for monophonic (sound emission of a single note), and therefore has the following problems in the case of polyphonic (sound emission of a plurality of notes) portamento by chord performance.
In polyphonic portamento, when a plurality of keys are pressed by chord performance, the pitch of a sound emitted by a previous key press is taken as a starting point, and a pitch change is made to the pitch of a sound to be emitted by a current key press. This polyphonic portamento is described with reference to FIG. 6. FIG. 6 is a diagram depicting the positions of a previous key press and a current key press performed on a key board, previous key-press timing, and current key-press timing.
In the example of FIG. 6, the sound of the key of a pitch C1 is emitted, and then a current cord performance of “C major” is performed by the keys of constitutive notes “C4 note”, “E4 note”, and “G4 note” being pressed in sequence. Here, first, as for the key press of “C4 note”, the C1 note is taken as a starting point of the C4 key press, and the pitch of the sound emission is changed from the starting point toward “C4 target”.
Next, as for the key press of “E4 note”, the pitch of the sound emission is changed toward “E4 target” from the starting point of the key press of the E4 note whose pitch is higher than the pitch of the C1 note, that is, the current pitch already heading toward “C4 target”. Next, as for the key press of “G4 note”, the pitch of the sound emission is changed toward “G4 target” from the starting point of the key press of the G4 note whose pitch is higher than the pitch of the second note, that is, the current pitch already heading toward “E4 target”. In these pitch changes, three constitutive notes (“C4 note”, “E4 note”, and “G4 note”) make the same pitch change, as depicted in FIG. 6. Therefore, there is no pitch difference among the constitutive notes, whereby the harmonic feeling is lost.
In order to address this problem, a technique has been suggested in which a plurality of previous key-press pitches are retained as history and, when a plurality of keys are simultaneously pressed, not only the latest key-press pitch but also the key-press pitch immediately before the latest key-press pitch and the key-press pitch before this key-press pitch are allocated to other starting points, whereby the harmonic feeling is kept during the pitch change (sound emission with portamento). This technique is described with reference to FIG. 7.
In FIG. 7, when a chord performance of “F minor” has been previously performed by pressing the keys of constitutive notes “C1 note”, “F1 note”, and “Ab1 note” in sequence, if a chord performance of “C major” is currently performed by pressing the keys of constitutive notes “C4 note”, “E4 note”, and “G4 note” in sequence, first, the immediately-preceding key-press pitch of “Ab1 note” is taken as a starting point for the key press of “C4 note”, and the pitch of the sound emission is changed from the starting point toward “C4 target”.
Next, as for the key press of “E4 note”, the pitch of the second preceding key press, that is, “F1 note” is taken as a starting point, and the pitch of the sound emission is changed from the starting point toward “E4 target”, on condition that the musical sound whose pitch is changing in response to the key press of “C4 note” has not reached “C4 target”. Moreover, as for the key press of “G4 note”, the pitch of the third preceding key press, that is, “C1 note” is taken as a starting point, and the pitch of the sound emission is changed from the starting point toward “G4 target”, on condition that none of the musical sounds whose pitches are changing in response to the key pressing on “C4 note” and “E4 note” have reached “C4 target” and “E4 target”.
By these pitch changes, pitch differences occur among the constitutive notes and whereby a harmonic feeling can be acquired. However, even when the chord performance of “C major” is currently performed by pressing the keys of the constitutive notes “C4 note”, “E4 note”, and “G4 note” almost simultaneously, the pitch differences among the constitutive notes during the pitch changes represent a minor chord, that is, F minor of C1/G1/Ab1.
That is, even when a major chord is played, the pitch is changed with a minor chord. Such change is a harmonically unfavorable detriment. Also, if the chord performance of “C major” is performed such that each note is individually played, or in other words, if the chord is played such that the keys of the constitutive notes “C4 note”, “E4 note”, and “G4 note” are pressed in sequence at predetermined time intervals, the pitch differences among the constitutive notes during the pitch changes causes dissonance, and the harmonic feeling is disadvantageously lost, as depicted in FIG. 8.
Thus, in short, there is a problem in the polyphonic portamento based on the above-described technique in that a pitch change cannot be made with pitch differences among constitutive notes of a played chord being maintained.